Light control device

ABSTRACT

A light control device especially suited for use in traffic signal lights, having at least a pair of opposing light control elements defining an unobstructed channel, each of which elements comprises a series of broad, specularly reflecting surfaces alternately facing the input and output ends of the device. In one embodiment, the device comprises a plurality of vanes positioned parallel to each other, in which each vane has on a major surface thereof a plurality of planar specularly reflecting surfaces alternately facing the input and output ends of the device. The input facing surfaces are disposed at an angle such that light rays diverging from a given direction at an angle in excess of a given angle are obstructed. The output facing surfaces are positioned at an angle such that some divergent rays may be redirected, hence adding to the light output within the allowed divergent limits, while also cooperating with the input angled faces to block outward reflections of other divergent light rays. When used in a traffic signal device, side reflections are minimized, thus thwarting drivers outside controlled lanes, who would use such side reflections to anticipate signal changes.

United States Patent 91 Cobb, Jr.

[ July 8,1975

[ LIGHT CONTROL DEVICE [75] Inventor: Sanford Cobb, Jr., St. Paul, Minn.

[73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul,Minn.

[22] Filed: Sept. 24, 1973 [21] Appl. No.: 400,253

[5.2] US. Cl 240/4631; 240/41.35 R; 340/84 [51] Int. Cl. F2'lv 11/02[58] Field of Search 240/4631, 46.33, 46.35,

240/4l.35 R. 41.35 C, 41.35 D, 41.36, 240/103 R, 106 R, 78 LK; 340/74,84; 350/259, 276

d l I 445 ii /a Primary ExaminerSamuel S. Matthews AssistantExaminer-Alan Mathews Attorney, Agent, or Firm-Alexander, Sell, Steldt &DeLal-lunt [5 7] ABSTRACT A light control device especially suited foruse in traffic signal lights, having at least a pair of opposing lightcontrol elements defining an unobstructed channel, each of whichelements comprises a series of broad, specularly reflecting surfacesalternately facing the input and output ends of the device. In oneembodiment, the device comprises a plurality of vanes positionedparallel to each other, in which each vane has on a major surfacethereof a plurality of planar specularly reflecting surfaces alternatelyfacing the input and output ends of the device. The input facingsurfaces are disposed at an angle such that light rays diverging from agiven direction at an angle in excess of a given angle are obstructed.The output facing surfaces are positioned at an angle such that somedivergent rays may be redirected, hence adding to the light outputwithin the allowed divergent limits, while also cooperating with theinput angled faces to block outward reflections of other divergent lightrays. When used in a traffic signal device, side reflections areminimized, thus thwarting drivers outside controlled lanes, who woulduse such side reflectionsto anticipate signal changes.

14 Claims, 5 Drawing Figures LIGHT CONTROL DEVICE BACKGROUND OF THEINVENTION 1. Field of the INVENTION This invention relates to opticaldevices used to shield light directed through the device from beingscattered or reflected, thereby avoiding unwanted reflections. Inparticular, the invention relates to louver constructions for use withtraffic control signal lights, wherein light shields are desired toprevent drivers outside a predetermined angle, i.e., in another trafficlane, from seeing the signal light.

2. Description of the Prior Art The simple expedient of surrounding alight source with a shield extending outward from the source tocollimate the light and to restrict the line of sight thereof is wellknown. Such devices are generally provided with optically diffuse lightabsorbing surfaces to minimize reflections. Where such shields areprovided for use with traffic control signals, sideward reflections offthe shields may enable drivers in other lanes to anticipate changingsignals or to become confused as to allowable motion.

US. Pat. No. 2,701,298, discloses a light shield in which a plurality offlat, generally horizontal, thin shields are secured in a parallel,closely spaced relationship within a frame. The shield is intended to bemounted in front of automotive headlights to minimize upward reflectionsof the lights thereby preventing reflections, such as produced by fog,back into the drivers eyes. The surface of the thin shields are said tobe finished to be non-reflecting, however, in practice such surfaces doscatter appreciable quantities of light, rendering them unsuitable forcritical applications. Similar devices having a plurality of verticallypositioned parallel vanes are commercially available for use withtraffic signal devices.

SUMMARY OF THE INVENTION The present invention relates to an improvedlight control device which overcomes the shortcomings of theaforementioned prior art devices and which may be conveniently andinexpensively formed from molded plastic. The device has a light inputend and a light output end through which a beam of light may betransmitted in a given direction, and includes at least one pair ofopposing light control elements defining a channel. Each of the elementscomprise a series of broad, specularly reflecting surfaces alternatelyfacing the input and output ends, in which the angle formed between anyoutput facing surface and the given direction is greater than an anglewhose cotangent is the ratio of the length of the channel over thedistance between the elements at the output end, and less than 20, andin which the angle formed between any input facing surface and the givendirection is greater than 45. In a preferred embodiment, a plurality ofsubstantially planar vanes having the broad specularly reflectingalternately facing surfaces on major faces thereof are positionedparallel to each other within a cylindrical shell. The alternatelyfacing surfaces cause light from the beam which diverges from the givendirection by more than a desired angle to be obstructed.

A preferred use for such a device is a traffic signal light shieldadapted to be positioned in front of a traffic signal device to minimizeside reflections. In such a use, a plurality of vanes such as describedhereinabove are vertically positioned to intercept horizontally directedlight rays diverging from the given direction by more than a desiredangle.

Unlike prior art devices which rely on light scattering and absorptionto minimize transmission of light, the present invention utilizescontrolled reflection from precisely angled faces to either reflectdivergent light rays back to the input of the louver device or toreflect such rays several times until such rays are either absorbed orscattered so as to be sufficiently low in intensity as to be generallyundetectable. Accordingly, in the present invention the angled surfacesare smooth and reflecting to minimize light scattering therefrom. Lightscattering is further decreased by ensuring that the peaks between theinput and output angled faces are sharp, i.e., have a radius ofcurvature of less than 0.015 inches (0.4 mm). In operation, the louverdevices of the present invention when used in traffic signal devices areespecially useful in preventing motorists outside controlled areas fromanticipating their own signal changes by stealing the signal. Theadvantages of the present invention over prior art devices areespecially evident at night, when even low level side lighting due tounwanted reflections are more visible due to dark background conditions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of alouvered embodiment of the light control device of the present inventionutilized with a traffic signal light;

FIG. 2 is a sectional view of the light control device of FIG. 1 alongthe lines 2-2;

FIG. 3 is a partially broken away perspective view of a single vane foruse in the louvered embodiment;

FIG. 4 is a view of a half shell providing a pair of opposing lightcontrol elements and of partially broken away vanes which may be usedtogether with the shell; and

FIG. 5 is a cross section of two of the vanes used in the louveredembodiment, showing the projection of two light rays passing between thevanes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a traffic signallight 10 is shown in perspective, the signal light 10 having acylindrical visor l2, concentrically mounted within which is acylindrical louvered embodiment 14 of the light control device of thepresent invention. The device 14 is preferably constructed fromm twomating half shells 16 and 18, respectively, containing recessesfwithinwhich vanes 20, 22, 24 and 26 are positioned. The two half shells 16 and18 are designed to be secured together with adhesives or mechanicalfasteners prior to' insertion in the cylindrical housing 12.

The half shells 16 and 18 and vanes 20, 22, 24 and 26 are preferablymolded plastic constructions fabricated by injection molding a smoothsurface black plastic material such as polycarbonate. Such material isdesired in that it readily forms smooth surfaces which decreases lightscattering and improves specular reflections.

Inasmuch as the reflections from the arcuate interior surfaces of thehalf shells 16 and 18 are not as critical as the reflections off vanes20, 22, 24 and 26, it may be preferred to fabricate the half shells 16and 18 from a structural foam plastic material in order to produce aslight a weight construction as possible, even though such a material issomewhat less smooth, thereby producing some light scattering.Alternatively, the interior opposing flat portions 19 and 27, maycooperate to form a pair of opposing light control elements in themanner described hereinafter without vanes inserted therebetween, inwhich case the flat portions will preferably be as smooth as ispractical.

A cross section of the assembled louvered device 14 is shown in FIG. 2,taken along the lines 22. The half shell 16 is shown to have a pluralityof parallel recesses 28, 30, 32 and 34 each containing appropriateapertures into which projections on the respective vanes 20, 22, 24 and26 may be inserted, to position the vanes upon assembly of therespective components. The interior walls of the half shell 16 areshaped to have a series of angled bands, which bands alternately face aninput end 36 and an output end 38 of the shell 16. Accordingly, theinput angled bands 40 face the input end 36, while the output angledbands 42 face the output end 38.

Each major face of the vanes 20, 22, 24 and 26 has a series ofreflecting surfaces, each of which extends widthwise across the vanes.The surfaces alternately face toward opposite ends of the vanes.

A partially cut away view of vane 26 is shown in FIG. 3, to more clearlyshow the positioning of the alternately facing surfaces. Surfaces 45uniformly face the right side of FIG. 3, which, in the manner to bedescribed hereinafter, corresponds to the input end of the device, whilesurfaces 47 face the left of FIG. 3, i.e., the output end. Each vane isdesigned with mounting projections 46 and 48 to facilitate positioningthe vanes into the recesses 28, 30, 32 and 34 in the half shells l6 and18. The alternately facing surfaces 45 and 47 on opposite sides of eachvane are preferably staggered in the manner shown in FIG. 3 to allow thethickness of the vanes to be minimized, thereby minimizing both theextent of light blockage due to the vane and the weight thereof.Accordingly, when the vanes are assembled into the half shells l6 and18, it is preferable that alternate vanes be inverted from the positionshown in FIG. 3, such that the opposing surfaces on adjacent vanes arealigned to have the peaks and valleys between the input and outputfacing surfaces of one face in line with matching peaks and valleys ofthe opposing face. In an embodiment where the peaks and valleys are notstaggered,'no such inversion is necessary. When so inverting the vanes,care must be taken not to reverse the vanes, thereby facing the inputand output facing surfaces the wrong way. The projections 46 and 48 onthe vane 26 (the other vanes are similarly provided) and the aperturesin the recesses of the half shells 16 and 18 are designedso that whenthe vanes are positioned as shown in FIG. 3, i.e., with the projectionstoward the bottom of the vane, they may be inserted into recesses 30 and34 as shown in FIG. 2. Similarly, when the vanes are inverted such thatthe projections 46 and 48 are not at the top of the vanes, they may beinserted into the recesses 28 and 32.

In the cylindrical louvered embodiment shown in the FIGS. 1, 2 and 4,the vanes are designed to be equal length, i.e., the distance betweenthe input and output end of the louver device is the same. Inasmuch asthe subtended chord length within the shell varies with the position ofa vane within the shell, the width of the various vanes must be adjustedconsistent with the respective position of a given vane. In theembodiment shown in FIGS. 1, 2 and 4, vanes 20 and 26, and vanes 22 and24, respectively, are identical. The recesses 28 and 34 foraccommodating vanes 20 and 26, and the recesses 30 and 32 foraccommodating vanes 22 and 24 are thus positioned at equal length chordswithin the shell. Where a rectangular louver construction is utilized,the vanes may, of course, be of a uniform width and thus be completelyinterchangeable.

Inasmuch as the vanes are designed to controllably reflect, rather thanscatter light, it is important that the vanes be fabricated from amaterial having characteristics such that smooth, highly reflectingsurfaces, and sharp peaks between the faces are obtained. Injectionmolded black polycarbonate has been found exemplary in this regard. Thesharp peaks are especially desired to minimize light scattering from thepeaks. Thus, where injection molded components are utilized, specialcare is desirably taken to ensure that the radius of curvature along therespective peaks is less than 0.015 inches (0.4 mm). The radius ofcurvature in the corresponding valleys between the input and outputfacing surfaces is not subject to such limits in that light tends to betrapped in the valleys and does not appreciably contribute touncontrolled light scattering.

FIG. 4 is an exploded view of a substantially cylindrical half shell 16containing flat portions 19 and 27 which cooperate to form a pair ofopposing light elements, between which an unobstructed channel extendsfrom the input end to the output end. Each of the flat portions 19 and27 is provided with a series of broad, specularly reflecting surfacesalternately facing the input and output ends. In a preferred embodiment,each half shell 16 and 18 is provided with recesses 28, 30, 32 and 34into which may be inserted the vanes 20, 22, 24 and 26. In FIG. 4, thehalf shell 16 and vanes 20, 22, 24 and 26 are shown positioned with thevanes horizontal. In a traffic signal device such as shown in FIG. 1,the assembled shells and vanes are rotated to have the vanes positionedvertically so as to control horizontal lightscattering. The projections44, 46 and 48 on vanes 22 and 26 are shown in full in FIG. 4.

FIG. 5 is a sectional view of two vanes 50 and 52 disposed parallel toand adjacent each other, showing the manner in which light raysdiverging from a direction indicated by the arrow 53 by more than adesired angle are controllably reflected and thereby obstructed frompassing through the device.'The length of the vanes and the spacingtherebetween is such as to provide an aspect ratio, which is defined asthe ratio of the length, 1, of the enclosed channel and the spacing, d,between the elements at the output end, of slightly more than 4 to 1. Asmay be seen, the aspect ratio is the cotangent of the widest angle 55through which light may directly pass from the input to the output endof the adjacent louvers 50 and 52 without hitting either of the opposinglight control elements. In the present invention, the angle of the inputfacing surfaces 45, only a few of which are labeled in the interest ofclarity, are ideally to the direction 53 of light entering parallel tothe parallel positioned louvers 50 and 52. In practice, it is sufficientthat the angle of the input facing surfaces 45 be greater than 45, asmost divergent light rays will still be reflected several times acrossthe channel until sufficient absorption occurs as to effectivelyminimize the transmission of such divergent light rays. This reductionin the angle of the input facing surfaces 45 is desirable inasmuch as itenables a further reduction in the physical thickness and weight of thevanes. The angle of the input facing surface 45' is shown to be angle 58which is formed between input facing surface face 45' and the direction53.

The angle 64 of the output facing surfaces 47, only a few of which arelabeled in FIG. 5 in the interest of clarity, are designed such that thesurfaces nearest the output end 56 are shadowed from light entering atthe maximum angle 55. As shown in FIG. 5, the angle 55, the cotangent ofwhich is equal to the aspect ratio, is about 12 /2. Accordingly, theangle 64 of the output facing surfaces 47 is in excess of that angle.The angle 64 of the output facing surfaces 47 is here defined as theangle formed between an output facing surface 47 and the direction 53. x

The performance of the angled surfaces in controlling edge illuminationfrom divergent light rays is shown by the light rays 70 and 72, whichemanate from the light source 74. In prior art planar louver devices,light rays such as 70, which enter at an angle in excess of that angle55 associated with the aspect ratio, but less than some predeterminedangle, will be reflected once, at an angle in excess of the desiredviewing angle, and thus produce unwanted side glow. In contrast, in thepresent invention, some light rays such as 70 impinge on the inputfacing surfaces 45, and are thus either directly reflected back to theinput end 54 or are multiply reflected as shown. Light ray 72 isillustrative of divergent rays entering so as to strike the outputfacing surfaces 47, which rays are reflected out at an angle less thanthat angle 55 associated with the aspect ratio to enhance the totallight throughput of the louver device.

In an embodiment where the flat surfaces 19 and 27 of the half shells l6and 18 are used as the pair of light control elements, the resultingaspect ratio for the depicted geometry would require that the outputfacing surfaces be positioned at an angle greater than about 53. Sinceit is desired that the angle of the output facing surfaces not exceed itis evident that four such shells must be joined in series.

In the embodiments depicted herein, the pairs of light control elementsare all shown to be parallel to each other. It is also envisioned thatthe elements in some embodiments may be non-parallel, such that thedistance between the elements varies along the length thereof betweenthe input and output ends. In such a case, the angle of theoutput'facing surfaces must be greater than the angle whose cotangent isthe ratio of the length of the channel formed between the elements andthe distance between the elements at the output end.

It is standard practice in the traffic control-industry to utilizelouver devices having aspect ratios of 4/1 and 6/1. Accordingly, apreferred embodiment of the present invention provides the input andoutput facing surfaces at angles consistent with these practices. Theangle whose cotangent is 6 is approximately 9 /2", while that whosecotangent is 4 is approximately 14. To insure that the output facingsurfaces near the output end are wholly shadowed, it is furtherdesirable that the angle of the output facing surfaces 47 be in excessof such angles. Therefore, while the output facing surfaces 47 aredesirably between 6 and 20, a particularly desired construction utilizesthe output facing surfaces 47 angled at 16, thereby forming aconstruction in which the desired standardized aspect ratios are simplyobtained by appropriate selection of the length of the opposing lightcontrol'ele'ments.

Similarly, a preferred construction positions the input facing surfacesat 45 plus one-half the angle of the output facing surfaces. Thus, wherethe output facing surfaces are positioned at 16, the input facingsurfaces are positioned at 53. This preference ensures that divergentlight rays hitting an input facing surface such as shown by the lightray 70, are reflected at least three times soas to adequately absorb andscatter such light rays. a V

While it is preferable that the peaks and valleys on the opposingsurfaces of adjacent vanes such as and 52 be opposite each other, such apreference is not essential. Accordingly, while the angled surfaces onthe interior. of the shells l6 and 18 of FIG. 1 are desirably angled tomatch the angles of the surfaces on the vanes, it is not essential thatthe relative positions of the peaks and valleys on the shells correspondwith the positions of the peaks andvalleys of adjacent surfaces on thevanes.

Performance of the light control devices has been found optimum not onlywhen the radius of curvature of the peaks is as small as possible, butalso when the number of peaks is kept to a practical minimum. Since eachpeak reflects some light, the total scattered light reaching the outputend 56 is increased wherever the number of peaks is increased.

While only vanes having regularly alternating and staggered faces onopposing surfaces of the vanes are 'shown herein, a number of otherconstructions falling within the general guidelines set forthhereinabove may be employed. For example, a series of fins along thesurface of each vane may be utilized to form the peaks in lieu ofalternating input and output angled faces. Similarly, additional narrow,angled faces may be added at the valleys between the input and angledfaces to' improve mold release characteristics. Unwanted reflec'tionsproduced by such faces such .may be minimized by selective control ofthe angle of the faces and the radius of curvature at the intersectionbetween the faces and the input and output angled faces.

It is further envisioned that the louver devices may be constructedwithin the teachings of the present invention wherein-the vanes haveunequal lenghts, and

wherein the input and output angled faces within different vanes mayhave somewhat different angles. Louver devices may thus be constructedwherein adjacent louvers toward the extremities of the devicearedifferently spaced than those toward the center of the device so as toproduce different aspect ratios at various locations within the louverdevice. Alternatively, the various vanes within the louver device may beequally spaced, however, the aspect ratio may be varied by judiciousselection of the length of the various vanes and of the angles of theinput and output faces. Similarly, the angles of the input and outputfacing surfaces may be desirably varied along the length of each controlelement to optimize obstruction of light rays incident at varying anglessuch as impinge at varying distances along the channels.

From the foregoing description, the construction, operation and utilityof the light control device of the present invention will be apparent.The foregoing is considered as illustrative only of the principles ofthe invention. Further, since numerous modifications and changes willreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact construction and operation shown anddescribed. Accordingly, this particular modification and all othersuitable modifications and equivalents may be resorted to which fallwithin the scope of the invention as claimed.

1 claim:

1. A light control device having a light input end and a light outputend through which a beam of light may be transmitted in a givendirection, which device includes at least one pair of opposing lightcontrol elements defining a channel, each of which elements comprise aseries of broad specularly reflecting surfaces alternately facing saidinput and said output ends, the angle formed between any said outputfacing surface and said direction being less than 20 and greater than anangle whose cotangent is the ratio of the length of said channel overthe distance between the elements at the output end and the angle formedbetween any input facing surface and said direction being greater than45, which device obstructs light of said beam which diverges from saidgiven direction by more than a desired angle.

2. A device according to claim 1, further comprising a plurality ofsubstantially planar vanes positioned parallel to each other, majorfaces of which are shaped to form said series of reflecting surfaces.

3. A device according to claim 1, further comprising a substantiallycylindrical shell having interior flat portions forming a pair of saidopposing light control elements.

4. A device according to claim 3, further comprising a plurality ofsubstantially planar vanes within said shell, said vanes being mountedparallel to said flat portions, wherein major surfaces of said vanes areshaped to form said series of reflecting surfaces, opposing surfaces ofadjacent vanes and flat portions thereby forming pairs of said opposinglight control elements.

5. A device according to claim 4, said shell further having interiorcircumferential bands alternately facing said input and output ends, theangles of said bands matching those of the alternately facing surfacesof said vanes and flat portions.

6. A device according to claim 3, wherein said shell is a molded plasticmaterial, each half of said housing being identical to the opposite halfand being joined therewith to form the complete shell.

7. A device according to claim 1, wherein the angle between any outputfacing surface and said direction ranges between 6 and 20.

8. A device according to claim 7, wherein the angle of all output facingsurfaces is the same.

9. A device according to claim 8, wherein the angle between all inputfacing surfaces and said direction is approximately equal to 45 plusone-half of said angle formed between all the output facing surfaces andsaid direction.

10. A device according to claim 9, wherein the angle between all outputfacing surfaces and said direction is approximately 16 and the anglebetween all input facing surfaces and said direction length isapproximately 53.

11. A device according to claim 2, wherein each major face of said vaneshas a plurality of said alternately facing surfaces positioned such thatthe valleys between the adjacent input and output facing surfaces on oneface are displaced along the length of the vane from similar valleys onthe opposite face to decrease the thickness of the vane, therebyincreasing the light transmissivity of the device.

12. A device according to claim 1 1, wherein said valleys on one faceare centered approximately opposite the midpoint of the output facingsurface on the opposite face.

13. A device according to claim 1, wherein the peaks between adjacentinput and output facing surfaces have a radius of curvature of less than0.015 inches (0.4 mm).

14. A traffic signal louver device adapted to be positioned in front ofa traffic signal device to limit the angle of visibility of the signaldevice and to minimize side reflections of light emanating therefrom,said louver device having a light input end and a light output endthrough which a beam of light may be transmitted in a given direction,which device comprises a substantially cylindrical shell and a pluralityof substantially planar vanes vertically positioned parallel to eachother within the shell, opposing faces of adjacent vanes forming pairsof opposing light control elements defining channels, each of whichelements comprise a series of broad, specularly reflecting surfacesalternately facing said input and said output ends, the angle formedbetween any said output facing surface and said direction being lessthan 20 and greater than an angle whose cotangent is the ratio of thelength of said channel over the maximum distance between the elementsand the angle formed between any input facing surface and said directionbeing greater than 45", which device obstructs horizontally directedlight of said beam which diverges from said given direction by more thana de-

1. A light control device having a light input end and a light outputend through which a beam of light may be transmitted in a givendirection, which device includes at least one pair of opposing lightcontrol elements defining a channel, each of which elements comprise aseries of broad specularly reflecting surfaces alternately facing saidinput and said output ends, the angle formed between any said outputfacing surface and said direction being less than 20* and greater thanan angle whose cotangent is the ratio of the length of said channel overthe distance between the elements at the output end and the angle formedbetween any input facing surface and said direction being greater than45*, which device obstructs light of said beam which diverges from saidgiven direction by more than a desired angle.
 2. A device according toclaim 1, further comprising a plurality of substantially planar vanespositioned parallel to each other, major faces of which are shaped toform said series of reflecting surfaces.
 3. A device according to claim1, further comprising a substantially cylindrical shell having interiorflat portions forming a pair of said opposing light control elements. 4.A device according to claim 3, further comprising a plurality ofsubstantially planar vanes within said shell, said vanes being mountedparallel to said flat portions, wherein major surfaces of said vanes areshaped to form said series of reflecting surfaces, opposing surfaces ofadjacent vanes and flat portions thereby forming pairs of said opposinglight control elements.
 5. A device according to claim 4, said shellfurther having interior circumferential bands alternately facing saidinput and output ends, the angles of said bands matching those of thealternately facing surfaces of said vanes and flat portions.
 6. A deviceaccording to claim 3, wherein said shell is a molded plastic material,each half of said housing being identical to the opposite half and beingjoined therewith to form the complete shell.
 7. A device according toclaim 1, wherein the angle between any output facing surface and saiddirection ranges between 6* and 20*.
 8. A device according to claim 7,wherein the angle of all output facing surfaces is the same.
 9. A deviceaccording to claim 8, wherein the angle between all input facingsurfaces and said direction is approximately equal to 45* plus one-halfof said angle formed between all the output facing surfaces and saiddirection.
 10. A device according to claim 9, wherein the angle betweenall output facing surfaces and said direction is approximately 16* andthe angle between all input facing surfaces and said direction length isapproximately 53*.
 11. A device according to claim 2, wherein each majorface of said vanes has a plurality of said alternately facing surfacespositioned such that the valleys between the adjacent input and outputfacing surfaces on one face are displaced along the length of the vanefrom similar valleys on the opposite face to decrease the thickness ofthe vane, thereby increasing the light transmissivity of the device. 12.A device according to claim 11, wherein said valleys on one face arecentered approximately opposite the midpoint of the output facingsurface on the opposite face.
 13. A device according to claim 1, whereinthe peaks between adjacent input and output facing surfaces have aradius of curvature of less than 0.015 inches (0.4 mm).
 14. A trafficsignal louver device adapted to be positioned in front of a trafficsignal device to limit the angle of visibility of the signal device andto minimize side reflections of light emanating therefrom, said louverdevice having a light input end and a light output end through which abeam of light may be transmitted in a given direction, which devicecomprises a substantially cylindrical shell and a plurality ofsubstantially planar vanes vertically positioned parallel to each otherwithin the shell, opposing faces of adjacent vanes forming pairs ofopposing light control elements defining channels, each of whichelements comprise a series of broad, specularly reflecting surfacesalternately facing said input and said output ends, the angle formedbetween any said output facing surface and said direction being lessthan 20* and greater than an angle whose cotangent is the ratio of thelength of said channel over the maximum distance between the elementsand the angle formed between any input facing surface and said directionbeing greater than 45*, which device obstructs horizontally directedlight of said beam which diverGes from said given direction by more thana desired angle.